Hydraulic apparatus

ABSTRACT

A swashplate pump comprising a rotary cylinder block having cylinders disposed parallel to or inclined to the rotation axis and rotating on a valve, a swashplate adjacent the cylinder block to engage slippers attached to pistons which project from the cylinders in the cylinder block, and a central spring acting on a slipper plate which engages all slippers and urges them to the swashplate. The swashplate is supported by trunnion means whereby the swashplate may tilt to vary the stroke of the pistons in the cylinders and the trunnion means is so located that tilting movement of the swashplate to increase piston stroke will also increase the compression of the central spring thereby to increase the spring loading exerted by the slipper plate on the slippers.

United States Patent Boydell 1451 Jan. 25,1972

541 HYDRAULIC APPARATUS 2,292,125 8/1942 lfield 417 203 2,486,690 11/1949 Tipton ..91/475 [72] Inventor: Kenneth Raymond Boydell, Bredons Hard- 2 72095 3 195 Lucien et aL 9 75 X 119k, near Tewkesbury. England 2,733,666 2 1956 P811105 91 /475 x 73 nee: ow 3,096,723 7/1963 Puryear ..91/506 1 g 115;311:12 ffj Limited 3,108,544 10/1963 Pesce.. .417/203 3,208,395 9/1965 Budzich ...91/506 x 1 1 Filed: y 1, 1970 3,266,434 8/1966 McAlvay,... ...91/506 X [21] 3,396,670 8 1968 Baits ..91/504 Appl. No.: 33,720

Related U.S. Application Data Division of Ser. No. 694,717, Dec. 29, 1967.

Foreign Application Priority Data Feb. 23, 1967 Great Britain ..8,709/67 Sept. 26, 1967 Great Britain ..43,7l6/67 U.S. Cl ..91/475, 91/507 Int. Cl ..F0lb 3/00, F04b 1/26 Field of Search ..91/475, 504-506;

References Cited UNITED STATES PATENTS Primary ExaminerWilliam L, Freeh Attorney-Young & Thompson 57 ABSTRACT A swashplate pump comprising a rotary cylinder block having cylinders disposed parallel to or inclined to the rotation axis and rotating on a valve, a swashplate adjacent the cylinder block to engage slippers attached to pistons which project from the cylinders in the cylinder block, and a central spring acting on a slipper plate which engages all slippers and urges them to the swashplate. The swashplate is supported by trunnion means whereby the swashplate may tilt to vary the stroke of the pistons in the cylinders and the trunnion means is so located that tilting movement of the swashplate to increase piston stroke will also increase the compression of the central spring thereby to increase the spring loading exerted by the slipper plate on the slippers.

7 Claims, 2 Drawing Figures PATENTED Jmzsmz 636,818

sum 1 [IF 2 INVENTOR Klunzm R. Bwmu.

ATTORNEYS HYDRAULIC APPARATUS This is division of application Ser. No. 694,717, filed Dec. 29, 1967.

FIELD OF THE INVENTION This invention relates to swashplate pumps of the kind comprising a rotary cylinder block having cylinders disposed parallel to or inclined to the rotation axis, valve means cooperating with the cylinder block during rotation, and swashplate means located adjacent one end of the cylinder block for causing reciprocation of the pistons in the cylinders during block rotation. This kind of pump will hereinafter be referred to as a swashplate pump.

DESCRIPTION OF PRIOR ART It has been proposed in swashplate pumps to provide a central spring acting on a slipper plate which holds the slippers against the swashplate. However, in these prior art proposals the central spring exerts a fairly constant thrust on the slipper plate irrespective of the angular setting of the swashplate. If the angular setting of the swashplate demands a large piston stroke the force required to hold the slippers in contact with the swashplate when the associated piston is being pulled from its cylinder against inertia and suction forces is quite considerable. The object of the present invention is to arrange that the compression of the central spring in the swashplate pump may be increased with increase in piston stroke.

SUMMARY OF THE INVENTION In accordance with the present invention a swashplate pump comprises a rotary cylinder block having cylinders disposed parallel to or inclined to the rotation axis, valve means cooperating with the cylinder block during rotation, a swashplate adjacent the cylinder block, pistons in the cylinders, slippers universally pivoted one to each piston to project from the block to engage the swashplate, a central spring, a slipper plate located between the swashplate and the cylinder block to engage all slippers, universal pivot means between the central spring and the slipper plate whereby the spring load exerted by the central spring acts on the slippers to urge them against the swashplate, and trunnion means to support the swashplate for tilting movement to vary the stroke of the pistons within the cylinders, the trunnion means being so located that tilting movement of the swashplate to cause increased piston stroke will also increase the compression of the central spring thereby to increase the spring loading exerted by the slipper plate on the slippers.

The trunnion means may locate the swashplate to tilt about an axis which is offset from either the plane containing the pivot centers of attachment of the slippers to the pistons or offset from the rotation axis of the cylinder block or both.

A bearing around the cylinder block may locate the block for rotation in the casing and may be so positioned as to resist directly the side thrust applied to the cylinder block from the swashplate through the slippers and pistons.

BRIEF DESCRIPTION OF THE DRAWINGS A pump in accordance with one embodiment of the invention will now be particularly described with reference to the accompanying drawings in which,

FIG. 1 is a longitudinal cross section through the embodiment, and

FIG. 2 is a cross section taken on the line IIII of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawings, the structural member of the pump is an aluminum alloy casting and comprises two integrally formed parts indicated as the valve 1 and the casing 7. The valve 1 has a flat valve surface 2 which contains a main high-pressure delivery port 3 of conventional kidney shape. A high-pressure screw connection 4 is provided in the valve 1 extending from the main port 3 for attachment of a suitable pipe connection. A plurality of screw-threaded apertures (not shown) extend from a face 6 of the valve opposite to the surface 2. These screw-threaded apertures form the means by which the whole pump may be secured by bolts to the wall of a liquid reservoir or other suitable mounting.

The hollow casing 7 is open ended at the end thereof opposite to the valve.

With the casing 7 a cylinder block 8 of cast iron is located for rotation about the rotation axis AA. The cylinder block 8 includes a surface 9 resting on the valve surface 2. Within the block 8 there are five regularly spaced cylinders 11 all of whose axes are parallel to the rotation axis AA of the block. Each cylinder 11 includes a port 12 opening into the surface 9, the ports 12 being arranged to cooperate with the main port 3 during rotation of the cylinder block 8 about the axis AA. The ports 12 are arcuate in shape and each is arranged so that its center of pressure coincides effectively with the central axis of its cylinder 11. At a position remote from the surface 9, the cylinder block 8 is of enlarged diameter to support a cylindrical bearing surface 13 surrounding the cylinder block. The bearing surface 13 closely engages within a cooperating cylindrical bearing surface 14 formed in the interior of the casing 7.

Five passages 15 are formed within the cylinder block, one between each adjacent pair of cylinder. Each passage opens from the surface of the block remote from the valve surface 9 into an annular channel 16 defined between the casing 7, the cylinder block 8 and the bearing surfaces 13 and 14. A recess 17 is formed in the valve surface 2, the inner portion of this recess cooperating with the cylinder ports 12 so as to form an inlet port while the outer part of this recess opens into the annular channel 16.

The casing 7 remote from the valve 1 includes a pair of integral lugs 18 each of which is bored transversely, thus producing a pair of spaced apertures 20. A cylindrical shaft 19 is fitted through the apertures 20. Between the lugs 18 a swashplate 21 is mounted on the shaft 19 by means of a cylindrical bore 22 extending through it. The swashplate 21 includes a flat swash surface 24 facing the cylinder block 8.

Within each cylinder 11 a piston 25 and a compression spring 26 are located, the spring acting to urge the piston outwardly from the cylinder. Each spring 26 reacts against a washer located in a recess 22 at the end of the cylinder adjacent to the surface 9. At its outer end each piston 25 is formed with a universal pivot in the form of the spherical socket 27 and the enclosed ball 28. The ball 28 is integrally connected to a slipper 29 engaging against the swash surface 24. A hydraulic passage 31 within the piston gives access to the socket 27 for lubrication and also connects to the a passage in the ball which feeds liquid at pressure through a restrictor to a recess in the slipper surface in contact with the swash surface 24. The recess is of such size that the pressure loading applied to the slipper by the piston is almost completely balanced. Any other conventional system to hydraulic lubrication and/or balancing for the slipper may be employed.

A retaining plate 36 includes five apertures 37 engaged one on each slipper 29. Centrally, the retaining plate 36 reacts against a ball 39 carried by a pad 41 slidably mounted in a central bore 32 in the cylinder block. Within the bore 32 a central compression spring 43 is located which reacts from a shoulder 44 is the block to urge the pad 41, the ball 39 and the plate 36 towards the swashplate. The spring 43 thus serves to retain the slippers 29 in contact with the swash surface 24. The force exerted by the spring on the shoulder 44 will also serve to hold the cylinder block 8 against the valve surface 2 to ensure initial engagement.

A splined aperture 45 is provided centrally within the cylinder block to open into a comparatively large aperture 46 extending centrally through the valve 1. A drive shaft (not shown) may be inserted through the aperture 46 to engage the splined aperture 45 to drive the cylinder block. The engagement of the shaft in the splined aperture 45 should be loose to ensure that it can exert no side thrust on the block.

The pump as described is mounted for use on the wall of a liquid reservoir by means of screw-threaded bolts extending into the screw-threaded apertures in the valve. The drive shaft is arranged to extend vertically downwards through the wall of the reservoir to engage in the splines of aperture 45. An electric motor or other suitable driving means is located on the outside of the reservoir. Preferably the whole pump is located below liquid level in the reservoir. If the shaft passes through the wall of the reservoir below liquid level, a suitable seal is used,

The electric motor or other driving means normally provides a bearing to locate its drive shaft and in the present instance this bearing is sufficient to locate the drive shaft which extends into the aperture 45. In other words there is no need under most conditions to supply a special bearing housing for the shaft within the valve or other parts of the pump.

In operation, the cylinder block is driven by the drive shaft and the rotation of the block will cause reciprocation of the pistons in their cylinders by virtue of the fact that the slippers are held against the swashplate 24. As shown in the drawings the section through the valve is located at 90 to the section through the remainder of the pump in order to show the main port 3 and the recess 17. During rotation, liquid enters the pump through the open end of the casing the flows around and over the swashplate. This inlet liquid in the passages 15 is induced by a centrifugal pumping action to flow to the annular channel 16 where slight pressure is generated. From channel 16 liquid enters the recess 17 and has access to the cylinder ports 12 during the periods when their pistons are moving outwardly from their cylinders. A vane may be provided internally of the casing in the channel 16 to interrupt rotary flow of liquid and thus to increase the pressure within the channel. When cylinders connect with the main port 3 during block rotation and the pistons are urged into the cylinders, liquid is delivered at high pressure from the connection 4.

The fact that the swashplate is inclined causes considerable side thrust to be exerted on the cylinder block by the pistons being urged under pressure into their cylinders. For each piston under pressure the effective point at which the side thrust operates is the center of the ball joint. It is preferably arranged that the axial extent of the bearing surfaces is such that the lines of the action of the lateral forces exerted through the ball joints may pass directly through the bearing surfaces without creating tilting movement on the cylinder block.

In assembly of the pump described, the cylinder block is initially entered into the open end of the casing the pass through the bearing surface 14 to engage the valve surface 2. The pistons and slippers are then entered into the cylinders and the swashplate 12 is held between the lugs while the shaft 19 is passed through the trunnion bearings. As shown in FIG. 2 the shaft 19 is retained in position by spring clips 47 which engage in the grooves in the shaft 19 to act against washers 48 in turn engaging against lugs 18. Since, in use, the endwise thrust exerted on the shaft 19 is negligible, the spring clips are adequate to ensure that the shaft will remain in position. In order to adjust the angular displacement of the swashplate 18 about the shaft 19 a lever is attached in any convenient manner to the swashplate to extend to a control device.

In the assembly of the pump no screw-threaded locking devices need to be used thus reducing the cost of manufacture of the pump.

During each occasion that a piston 25 is urged out of its cylinder, the force which urges the piston from its cylinder and also maintains the associated slipper 29 in contact with the swash surface 24 is supplied by the compression of the cylinder spring 26 and by the compression of the central spring 43 which acts through ball 39 and slipper plate 36 on to the associated slipper 29. Where a piston on its outward stroke is operating to induce liquid at low pressure to enter the cylinder the moving force supplied by the two springs 26 and 43 must be sufficient to accelerate the piston and slipper outwardly and to suck liquid into the cylinder. The boost pressure available in the recess 17 will of course assist in urging liquid into the cylinder. Where a small piston stroke is selected by virtue of a small angle for the swashplate 21 the acceleration force to move each piston and slipper assembly outwardly is not very large and is adequately supplied by the compression of the cylinder spring 26 and the central spring 43. With increase in the selected piston stroke (assuming constant speed drive of the pump) the acceleration force to move each piston and slipper combination outwardly will increase with increase in stroke. The present invention provides that the spring force available to accelerate each piston and slipper combination outwardly will increase with increase in selected piston stroke by so selecting the position of the trunnion shaft 19 that it is offset from the rotation axis A-A by a small distance X towards the part of the swashplate corresponding to the outermost positions of the pistons during reciprocation and is offset from the plane of the ball joint centers away from the cylinder block by a distance Y. Since a single shaft 19 for the trunnion is employed it is clear that this shaft must be offset from the plane of the ball joint centers at least to the extent that it does not break into the swash surface 24. The swashplate 21 is conveniently provided with limiting stops which limit the range of displacement adjustment from maximum in the position shown in FIG. 1 to an almost zero angle. For the maximum displacement the stop is effectively determined by the edge of the slipper plate 36 coming very close to and possibly touching the end surface of the cylinder block. The minimum displacement position of the swashplate is determined by the lug 50 on the casing which is adapted to make contact with a cooperating projection 51 of the swashplate.

Assume now that the swashplate has been moved through an angle S from its zero displacement condition. The offset X will now have caused an inward displacement of the ball 39 which may be easily shown to be (X tan S). At the same time the offset Y will have caused a further displacement of the ball 39 by an amount which can be shown to be (Y sec S-Y). The total inward movement of the ball 39 is the sum of the two amounts mentioned above and will produce further compression of the spring 43 with increase in swash angle. The further compression due to the offset Y is extremely small for small swash angles, but the compression due to the offset X increases substantially in proportion to the swash angle at small swash angles.

During operation of the pump the force from spring 43 operates through the slipper plate 36 directly on the slippers 29 and where a piston is moving outwardly from its cylinder the compression force of spring 43 is preferably arranged so as at least to hold the slipper on the swash surface 24 and thereby provide the acceleration for the slipper. The cylinder spring 26 is preferably of sufficient strength so as to urge the piston outwardly and to hold it in compressive contact with its cooperating ball 28. With increase in selected swash angle the compression of the spring 43 will increase thus giving a greater force to the slipper plate to hold the slippers in contact with the swash surface 24. Thus with increased swash angle the extra compression applied to the central spring 43 will help to provide the extra force necessary to urge each piston and slipper combination outwardly to retain a contact with the swashplate surface 24.

I claim:

1. A swashplate pump comprising a rotary cylinder block having cylinders disposed parallel to or inclined to the rotation axis, valve means cooperating with the cylinder block during rotation, a swashplate adjacent the cylinder block, pistons in the cylinders, slippers universally pivoted one to each piston to project from the cylinder block to engage the swashplate, a central spring, a slipper plate located between the swashplate and the cylinder block to engage all slippers, universal pivot means between the central spring and the slipper plate whereby the spring load exerted by the central spring acts on the slippers to urge them against the swashplate, the trunnion means to support the swashplate for tilting movement to vary the stroke of the pistons within the cylinders, the trunnion means being so located that tilting movement of the swashplate to cause increased piston stroke will also increase the compression of the central spring thereby to increase the spring loading exerted by the slipper plate on the slippers.

2. A swashplate pump as claimed in claim 1 wherein the trunnion means in located such that the trunnion axis is offset from the rotation axis towards the part of the swashplate corresponding to the outermost positions of the pistons during their reciprocating motion.

3. A swashplate pump as claimed in claim 1 wherein the valve means has a flat valve surface on which the block rotates and the spring means reacts on the block to urge the block against the flat valve surface.

4. A swashplate pump as claimed in claim 1 including a structural member formed in one piece and having a flat valve surface formed thereon, an internal cylindrical surface formed therein to engage the cylinder block to react the side thrust exerted on the cylinder block by the swashplate, and bearing apertures to engage the said trunnion means.

5. A swashplate pump as claimed in claim 4 wherein the structural member is formed of an aluminum alloy and the cylinder block is formed of cast iron.

6. A swashplate pump as claimed in claim 5 wherein the trunnion means comprises a single shaft passing through the said bearing apertures and through an aperture in the swashplate, the said shaft retaining the swashplate, the cylinder block and pistons in their operative positions.

7. A swashplate pump as claimed in claim 6 wherein the structural member includes a central aperture extending through the central portion of the valve surface and the cylinder block includes a splined central recess such that a loose driving shaft may extend through the central aperture into the recess.

t t I i t 

1. A swashplate pump comprising a rotary cylinder block having cylinders disposed parallel to or inclined to the rotation axis, valve means cooperating with the cylinder block during rotation, a swashplate adjacent the cylinder block, pistons in the cylinders, slippers universally pivoted one to each piston to project from the cylinder block to engage the swashplate, a central spring, a slipper plate located between the swashplate and the cylinder block to engage all slippers, universal pivot means between the central spring and the slipper plate whereby the spring load exerted by the central spring acts on the slippers to urge them against the swashplate, and trunnion means to support the swashplate for tilting movement to vary the stroke of the pistons within the cylinders, the trunnion means being so located that tilting movement of the swashplate to cause increased piston stroke will also increase the compression of the central spring thereby to increase the spring loading exerted by the slipper plate on the slippers.
 2. A swashplate pump as claimed in claim 1 wherein the trunnion means in located such that the trunnion axis is offset from the rotation axis towards the part of the swashplate corresponding to the outermost positions of the pistons during their reciprocating motion.
 3. A swashplate pump as claimed in claim 1 wherein the valve means has a flat valve surface on which the block rotates and the spring means reacts on the block to urge the block against the flat valve surface.
 4. A swashplate pump as claimed in claim 1 including a structural member formed in one piece and having a flat valve surface formed thereon, an internal cylindrical surface formed therein to engage the cylinder block to react the side thrust exerted on the cylinder block by the swashplate, and bearing apertures to engage the said trunnion means.
 5. A swashplate pump as claimed in claim 4 wherein the structural member is formed of an aluminum alloy and the cylinder block is formed of cast iron.
 6. A swashplate pump as claimed in claim 5 wherein the trunnion means comprises a single shaft passing through the said bearing apertures and through an aperture in the swashplate, the said shaft retaining the swashplate, the cylinder block and pistons in their operative positions.
 7. A swashplate pump as claimed in claim 6 wherein the structural member includes a central aperture extending through the central portion of the valve surface and the Cylinder block includes a splined central recess such that a loose driving shaft may extend through the central aperture into the recess. 